When patients are being mechanically ventilated on an intensive-care ward, for example, the patient to be ventilated is connected pneumatically to the ventilator or respiratory apparatus by a system of ventilation tubing. Because the breathing gas delivered to the patient must be adjusted with respect to temperature and humidity to meet the physiological needs of the patient, a respiratory humidifier is arranged in the inhalation or inspiration tube to heat and humidify the breathing gas. The respiratory humidifier comprises a liquid container filled with distilled water, through which the inhalation or inspiration gas is conducted and humidified.
The heating of the liquid in the liquid container is usually accomplished by means of a heating plate in the bottom part of the housing of the respiratory humidifier, wherein the heat is transferred from the heating plate to the thermally conductive bottom of the liquid container. The temperature of the breathing gas is measured by suitable sensors as it flows in and out, for example.
To avoid the liquid container running dry, the level of the liquid in the container is monitored. If the level falls below a minimum value, liquid from an external reservoir is supplied by way of a float valve, for example. No signal is given to the user to draw his attention to the need to add more liquid and possibly to replace the reservoir.
It is also known that respiratory humidifiers can be equipped with user interfaces, which comprise display elements and operating elements. A control unit regulates or automatically controls the function of the respiratory humidifier and if necessary emits an optical or acoustic signal when a functional state meriting an alarm is present. Because of the small dimensions of the control unit, there is only a limited capacity to provide a clear, optically recognizable signal, e.g., a signal generated by small LEDs forming the display elements.
Another requirement on a respiratory humidifier is that, because the liquid container is a medical-grade, single-use/disposable article, it must be possible to manufacture it especially easily and inexpensively. A design or structure for providing illumination, therefore, should not be too complicated, should comprise the smallest possible number of components, and be manufacturable at reasonable cost.
It is therefore the object of the present invention to provide a lighting device for a respiratory humidifier which can signal the presence of an alarm state in very clear optical fashion in as many directions as possible and which can be realized inexpensively on the basis of a simple design.
This object is achieved by the features of claim 1. Advantageous elaborations and embodiments are described in the subclaims.